FIG. 7 is a cross sectional view of a conventional mechanical sealing device, and FIG. 8 is an enlarged view of VIII portion of FIG. 7.
As a mechanical sealing device for sealing high pressure refrigerant like CO2, for example, a mechanical sealing device 100 shown in FIG. 7 has been known conventionally (for example, refer to Patent Document 1). This sealing device 100 comprises a mating ring 110 hermitically fixed to a housing 300, a seal ring 120 rotating with a rotary shaft 200 and sliding closely contact with the mating ring 110 and an O-ring 130 equipped between the seal ring 120 and the rotary shaft 200.
In this mechanical sealing device 100, even in case that the rotary shaft 200 moves to a thrust direction, a wavespring 140 energizes the sealing ring 120 to the mating ring 110 side, the sealing ring 120 follows the mating ring 110 along the thrust direction. Therefore, the sealing ring 120 closely contacts with the mating ring 110 constantly.
However, due to CO2 refrigerant is high pressure, as shown in FIG. 8, there is sometimes the O-ring 130 pushed to atmosphere Q side bites into a space g formed between the seal ring 120 and the rotary shaft 200. When the rotary shaft 200 moves to thrust direction in a status that the O-ring 130 bites into the space g, the sealing ring 120 also moves according to the moving of the shaft, as a result, there is a case that preferable sealing effect cannot be maintained due to a betweenness of the mating ring 100 and the sealing ring 120 widens.
Also, since a rubber constitutes the O-ring has a character that CO2 as refrigerant can easily permeate, the refrigerant permeates the O-ring and flows into atmosphere Q side, there is a case that preferable sealing effect cannot be maintained.    Patent Document 1: Japanese Unexamined Patent Publications No. 2001-221344